Weekend gym rats might be onto something. Weekend warriors, who put recommended amounts of exercise into one or two gym sessions（时段）, experience similar health benefits to those who work out several times a week, according to a new study. And those benefits include a longer life. “It is encouraging news that working out in just one or two days per week is connected to a lower risk of demise, even among people who do some activities but don't quite meet recommended exercise levels,” the lead researcher Emmanuel Stamatakis says in a statement.

    The World Health Organization recommends that adults perform two and a half hours of moderate-intensity（中等强度的）physical exercise, or an hour and 25 minutes of more energetic exercise per week. Usually this is done within several days, with experts suggesting that adults get up to 30 minutes of regular exercise each day. However, the new study suggests that busy people may be able to meet the standards when they have more free time, such as at weekends, and stay healthy all the same.

    Researchers studied data from more than 63,000 men and women in England and Scotland, including data about their activity habits and risks for death. The researchers put each individual in one of four groups: those who described themselves as inactive, those who exercised but less than what was recommended, those who exercised in the “weekend warrior” style, and those who worked out regularly more than three days a week.

    Adults who exercised in the “weekend warrior” style had a 40 percent lower risk of cardiovascular（心血管的）disease and a 30 percent lower risk of death by any cause than those who did not exercise at all. The lower risks of cardiovascular disease and overall death were similar to the risks of people who worked out regularly over the week.

    But take a pause before you give up your weekday gym habit. Just a couple of light sessions won't be enough to get benefits: “Weekend warrior” exercise sessions are usually 75-minute energetic workouts, according to the study.

    The results are promising overall, if you just simply can't fit physical activities into most days. The key here is that exercise is truly a lifeline（救生索）: It reduces your risk of illnesses like heart disease, diabetes, cancer and depression, according to the WHO. So, if you are just too busy on weekdays, let go of the guilt（内疚）. Just make sure to hit the gym hard at weekends.

人们将男、女体细胞内的染色体进行整理，形成了下列的排序图．请分析回答：

    With air pollution making much difference to many of Chinese cities, parents are calling for the installation(安装) of air cleaners in classrooms. There has been much debate over whether air cleaners should be used in China's schools. Some parents have donated cleaners to their children's classrooms, while others raise money together to make the purchase(购买). “Our school bought air cleaners last year. We did a little fund raising, with each parent throwing in several hundred for that,” said one parent.

    However, the idea of installing air cleaners for all the classes has been refused by some schools. Liu Liangcheng, vice-principal of Beijing's Taipinglu Primary School, says installing air cleaners bought by parents may lead to problems. “We have refused air cleaners bought by parents before, as there are clear and strict rules against educational fees. We can't just break the rules here. And without standard guidance (指示) from local authorities(权威部门), it is hard to decide on the brand of the cleaner, installation and even safety of the device(设备).”

    Moreover, experts say air cleaners can cause other health problems. Deng Gaofeng who works for the China Academy of Building Research says. “ In the classroom, if we keep windows and doors closed, the concentrations (浓度) of CO₂ will double from 1,000 PPM to some 2,000 PPM. According to national safety standards, the highest level should not be more than 1,500.” In addition, experts say air cleaners on the market are mostly designed for homes or offices. Evaluation(评估) is needed to know whether they are suitable in classrooms.

    It seems whether air cleaners should enter China's schools is an ongoing question. It still requires a more detailed plan.

阅读以上信息，用恰当的单词完成下面的表格，每空一词。

Topic : Should air cleaners be installed for students in school?

金丝猴是国家保护动物，其体内的血液只能从心房进入心室，从心室进入动脉，由动脉流经全身的毛细血管，再由静脉刘辉心房，而不能倒流，原因是（    ）